By way of background, and not by way of limitation, reference may be had to vehicular supplemental restraint systems wherein occupants are protected by inflating gas bags in the case of serious collision.
In some systems, bags are inflated from a gas storage bottle. However, whenever there is insufficient gas in the bottle, such as because of long-term leakage or gas migration through the bottle wall, there is inadequate inflation of the gas bag with consequent insufficient protection to the vehicle occupant in emergencies.
In consequence, almost all so-called "air bag" systems now use gas generators which typically involve setting off explosive charges for inflating bags upon sensing a serious collision. However, variations in bag inflation, such as due to differences in volume and pressure of generated gases, is a problem. Ambient temperature variations affect both bottled gas and generated gas systems. If gas pressure is excessive, such as due to high environmental temperatures affecting bottled gas and explosive charges, occupants are thrust back so violently by the inflating bag as to cause injury. Bag tearing or bursting also occurs from overpressure or overly rapid bag inflation.
In the case of gas generation with explosive charges, some relief was sought by venting excess gas during the inflation process. However, this created a hazard of venting obnoxious gases into the vehicle interior. Worse yet, escaping hot explosive gases would burn occupants. In desperate attempts to avoid such problems, gas exhaust passages were provided through firewalls of vehicles between the engine and the driver's or passenger's compartment. This, however, is a dangerous practice, since firewalls are there to protect drivers and passengers from flames bursting out from a damaged fuel supply or engine and, therefore, should not be penetrated by gas escape conduits that are rarely and hopefully never used.
Moreover, in various fields where bottled gas is used, there is a lingering uncertainty about the actual volume of gas left in the bottle or about the tightness and other i1 condition of the bottle and associated structure. Mere pressure sensing of the compressed gas in the bottle is inadequate in some situations, since gas volume and thereby pressure vary with temperature. In consequence, gas bottles are sometimes taken out of service or desired services are not performed, when there in fact (a) is nothing wrong with the bottle and its valving, while (b) there still is sufficient gas volume left in the bottle for its given task or, conversely, (c) operations are initiated with a bottle whose compressed gas content has in fact become inadequate for the task.